1. Field of the Invention
The present invention relates to a method for mounting a length measuring device, as well as the corresponding length measuring device itself.
2. Description of the Related Art
Such length measuring devices are used for example, as linear distance measuring devices in automation technology or for testing devices. Length measuring devices are also used on machine tools in very many cases. It is necessary there to measure the length of the carriage in relation to the machine bed with great accuracy. For this purpose the housing containing the scale graduation is fixedly screwed to the machine bed, for example, and the scanning unit of the length measuring device is connected with the movable carriage of the machine tool.
Often the length measuring devices are delivered as pre-assembled units, which means that the scale and the scanning unit, which can be moved in the measuring direction, are located together in one housing. Length measuring devices of this type are called closed, or encapsulated length measuring devices. But there are also so-called open length measuring devices, wherein the scanning unit and the scale are delivered separately.
It is necessary in both cases to align and fasten the housing, or the scale, with the greatest possible parallelism with respect to the measuring direction of the support, for example a machine tool.
In what follows, length measuring device is defined as a closed, as well as an open length measuring device. It is thus possible by the present invention to align and mount either only a scale, or a scale with a scanning unit, or a scale in a housing with a scanning unit contained therein.
Because of the continued improvement of the measuring accuracy of such length measuring devices, a correspondingly matched mounting accuracy with respect to their alignment by customary techniques becomes more and more elaborate. Measuring accuracies of ±5 μm or less are quite customary with such length measuring devices. Therefore the time required for the appropriate exact adjustment of the devices in the course of the mounting operations, for example on machine tools, is relatively great. Moreover, the mounting, or adjusting process itself is very difficult for a single assembler, particularly in connection with length measuring devices of some length.
A method and a device intended for mounting a scale or a scale support on an appropriate machine element are described in DE 199 14 311 A1. So that an undesired adhesive contact prior to the end of the alignment of the scale is prevented, spacers are proposed in this document, so that the scale can be definitely adjusted before it comes into contact with its support.
In DE 37 15 908 C2, a flexible scale with magnetic holders or suction cups is fastened on a body to be measured. This fastening which can be released relatively easily is also used during the measuring process itself. The disadvantage of this invention is that a permanent precise fixation of the scale is not possible in any way.
The same applies to published patent application EP 0 922 927 A2, wherein a magnetic fixation on the body to be measured is provided for the measuring process. There, too, the length measuring scale is not permanently brought into contact with the measuring body, and relatively low demands are made on the measuring accuracy.